In manufacturing processes of semiconductor devices such as DRAMs or microprocessors, plasma etching and plasma CVD are widely used. One of the issues in the manufacturing processes of semiconductor devices is to reduce the number of foreign particles attaching to a sample to be processed. For example, in a semiconductor manufacturing apparatus for etching, if foreign particles fall on a fine pattern of a sample before etching, the region is locally hindered from being etched. This causes a failure such as breaking of wire and reduces the yield. On this account, there have been contrived a number of methods for preventing foreign particles from attaching to the sample in the semiconductor manufacturing apparatus and a semiconductor inspection apparatus for inspecting the sample in the course of the manufacturing process. For example, Japanese Patent Application Laid-Open No. 8(1996)-64582 describes a method for installing a gas diffuser to prevent the fly-off of foreign particles during venting in a lock chamber for switching between a vacuum and the atmosphere. In this context, the term “venting” refers to switching from a vacuum to the atmosphere by purging nitrogen gas or the like. The gas diffuser prevents a rapid gas flow in a specific direction, and is disclosed, for example, in Japanese Patent Application Laid-Open No. 8(1996)-64582.